Method of manufacture of calcined aluminum fluoride

Abstract

The invention relates to a method of manufacturing calcined aluminum fluoride, AlF3, from aluminum fluoride hydrate, especially aluminum fluoride trihydrate, AlF3.3H2O, by drying and calcining. It is characterized in that (1) the hydrate is pre-dried or pre-calcined, (2) the pre-dried or pre-calcined hydrate is freed of the fine portion and (3) is totally dehydrated and calcined. The advantage of the method lies in the prevention of adhesions on the walls of the calcining apparatus, which restrict transmission of heat, which hitherto made continuous operation impossible, and in the increase of the purity of the product produced. A variation of method lies in the fact the fine component arising from the second method step is prepared into a coarser material, possibly added again to the product of the second method step which is free of fine component, and according to the third step of the method is dehydrated and calcined.

What is claimed is: 
     
       1. A method of manufacturing dust-free aluminum fluoride from aluminum fluoride hydrates comprising: drying the aluminum fluoride hydrate so as to partially dehydrate said aluminum fluoride hydrate;   separating out the fines of the partially dehydrated aluminum fluoride hydrate from the partially dehydrated aluminum fluoride hydrate;   drying and calcining said partially dehydrated aluminum fluoride hydrate by heating said partially dehydrated aluminum fluoride hydrate to a temperature of between 500° to 600° C. within 45 minutes so as to completely dehydrate and calcine same; and   mixing the fines of the partially dehydrated aluminum fluoride hydrate with a metastable aluminum fluoride solution so as to coarsen said fines.   
     
     
       2. A method according to claim 1 wherein the fines of the partially dehydrated aluminum fluoride hydrate have a particle size of ≦60 microns. 
     
     
       3. A method according to claim 1 wherein the fines of the partially dehydrated aluminum fluoride hydrate have a particle size of ≦40 microns. 
     
     
       4. A method according to claim 1 wherein the coarsened fines of the partially dehydrated aluminum fluoride hydrate is dried and calcined so as to completely dehydrate and calcine same. 
     
     
       5. A method according to claim 1 including the step of providing a disc drier for partially dehydrating said aluminum fluoride hydrate. 
     
     
       6. A method according to claim 1 including the step of providing an indirectly heated rotary furnace for completely dehydrating and calcining said partially dehydrated aluminum fluoride hydrate. 
     
     
       7. A method according to claim 1 including the step of providing a pneumatic conveyor drier for partially dehydrating said aluminum fluoride hydrate. 
     
     
       8. A method according to claim 1 including the steps of providing an air screening for separating out the fines of the partially dehydrated aluminum fluoride hydrate. 
     
     
       9. A method according to claim 1 including the step of providing cyclones for separating out the fines of the partially dehydrated aluminum fluoride hydrate. 
     
     
       10. A method according to claim 1 further including the step of extracting said fines of the partially dehydrated aluminum fluoride hydrate by means of a fabric filter. 
     
     
       11. A method according to claim 1 wherein the aluminum fluoride hydrate is in the range of hydrates AlF 3 .3H 2  O and AlF 3 .0.3H 2  O.